Process for recovery of nuclear fuel from used fuel elements



Nov. 7, 1961 FROM USED FUEL ELEMENTS Filed April 24, 1956 2 Sheets-Sheet1 HOT FUEL ELEMENT ZIRCONIUM OR ZIRCALOY CLADDING URANIUM ISOTOPES PU239Zr, |g,X8,Kr

STORAGE RARE EARTHS NH4F SOLUTION Cs, Sr, Ba.

" SOLUTION 0F NH F 4 NH4F BATH was 2? V DECLAD NH4OH HOT FUEL ELEMENTH2O GASES URANIUM ISOTOPES IZ'HZ, NH3 239 I '1 21 1 Kr RARE EARTHSZr(OH) -|NSOLUBLE Cs, Sr, Ba. SOLUTION NH4F,NH3

J: I 'NH4F BATH FILTER T SOLUTION U-Zr NH4F,NH5 2 OH) msoLuBLE NHSOLUTION 4 RARE EARTHS 3 T l Pu, Cs, Sr, Ba.

r STRIPPING a {r CONCENTRA'N CALC'NE FILTER r k NH4F SOLN. ZrOz 1 T RAGERODUCT SOLUBLE U,Zr 5T0 P NH4F SOLID INSOLUBLE NH4F RARE EARTHS COOLINGfi B H2O, HNO3 SOLUTION NH4F OxAL'C g g g CRYSTAL; R.E.,Cs,Sr, Bo.SOLUTION 1' NH: FILTER CRYSTALS U,Zr FILTER SOLUBLE Zr INSOLUBLE WATERINSOLUBLE u. RADlOACTIVE SLUDGE SOLUTION (NH4)3 ZrF Pu OXALATE SOLN.PRODUCT FILTER INVENTORS F ANDREW T. Me com) URANIUM FLUORIDE PRODUCTATTORNEY Nov. 7, 1961 A. T; MOCORD ET AL 3,007,769

PROCESS FOR RECOVERY OF NUCLEAR FUEL FROM USED FUEL ELEMENTS Filed April24, 1956 2 Sheets-Sheet 2 INVENTORS ANDREW T. Mc CORD DONALD R. SPINKATTORNEY United States atet v ERQMUSED FUEL ELEMENTS; AndrewAmherst,"N;Y.-, assignojrs to "The carboi'unduin {Tom arry; Niagara-Fall's} NzYz, a coi'porati'o'n of Delaware" This inviention relates we po for the rec very of T nuclear ifuel materials of either fissionable orfertile character from used or-spent -nuclear fuel elements.

Nuclear power fuelelements-can be divided-inte im,

nu-merable: types. The present; invention is primarily concerned withthose nucleanfuel elements ofthesolid clear 'fuel material, both ofwhich are valuable and must I be recovered. It is- -'essential that'l-the'fuel element" contain-fissionalflle nuclear fuell material; suchasithe urainium isotopes U- 233 and U 235, or'plutonium Pu-239.- Fuelelements; also contain nuclear fuel mater-ialsttliat :are not:originally vfissionable': but canbe;-converted to fissionable materialand :are therefore said 7 to -be- -fertile:?or-potent-ial nuclear fuelmaterials.

amountsJin' fact up to 993 %-'of the total uranium redntent inf-the'case of anunenriched"element:' During the course ofuse ot "the elementllli'ih' 'power" reactor the fissionable material, such as U 233 and U235 or Pu239 releasei'neutronsi Some of'thernutrons are tra' iped by thefertile but unfissionable U 238 "present-intheelement an'drthe [T -238eventually becomesPu 239' which is fissionalble 'Inrthe x samewaymhorium which isa fertile but unfissionable materialabsorbs'neutrdnsto' become U: 233 whichfiis fissionable and useful a"nuclearfuel material;

Fuelelmentsofthe soli'd typ'e' with whioh the prsent" invention isconcerned deteriorate dueto' radiation dam ag'e long' before theircontent'of fissionable fuel is used. At -the-same tinie ra'dibact-ive'fission broducts accumulate in fuel-e leme 'rit2" Someare'gas'es,"otli'efs'are' solids; s Dbjec-tion'abIe in tedu'c'in' he efiiciency ofi the reactor asa wlicl and'zeacli exerts 'some' 'part in thedestructionor*tlisintegration ofthe fuel'element. Long-be fore' thenuclear fuelj or fissionable material, has 'b'e'en "r: MeCord,' Snyder;andiDon ald Ri s iinlgnse V For example,- "U 238 is =a 'fertile materialoften present: in? -fuel -el'ements "in considerablecompletelywonsumed;the elements are adjudged to'be burned Fout? or spentand ar'e removed fromthereactoi"; Fofiresseritiali reasons i-ofieconomyzit is obviou's that the residual: unused iur'anium or *othernuclear fuel" materials, eithifertile or 'fissionab le contained in the"element be recovered:for iurrher'use:

None of the heretofore' known :methods for recovering fuel antlfertileurani-um or-thbriutn ifromflburn'ed out fuel elemente 'hasflbeencompletelysatisfactory For example; one?eriistingimethodforrecoveryTof'nuclear fuel material fuel lement assembly ismelted'arid slagge d; 'thesl' g'congj tainingthe objectionableradioactive fission prod'ucfts. Still another which has 'been' used''calls' er the dissolution or the usec l element inamolteniiuoiiclebath; inthe presenceof hydrofluoric-acid wherefluorine'gas' is added to'yield r-att re u anium heiaflueri e,rhehexafluoride is scrubbed with molten sodium fluoride to purify] itwhereupon the heitafluoride is then reduced to'tlie ura Ilium-metal. h IIt is an object of the present invention to provide improved method ofrecovering: nuclear 'fuel 'm'aterial's' from used fuel elements.. a I-tis a further object ofth'e present invention to videa-method ofrecovering both the fertile and'tlie' sionable nuclear fuel materialsfrom used fuel elements without theme of highly acid or'stronglycorrosive solutionsI v t v l .l l rar tii tann o i t .P q 1 1' h6d., we;efficient stripping of; corrosion resist ant claddings from the cores ofclad nuclear fuel elements.

It s a still further object of the pr sei 't nemia t uq c s t whe einhe. fiifiE-fiid? llYie is h f l ment e. nu e s n 9f n l ar. e f- 1material, both fertile and fissionable,;and radioactive ssi br wflvct oft e u e! e men webs-ven ra ed, and the usable materialsthereinextractediand recoveredfor further use.

These and e a i en a sand c i e il ri in a mm, the presentinvention willbecome apparent as the descrip- Q .:Pf9 d -11../.. .-L=,.- ii. .H. I

.We. av sd sw red-tha s an a l n i t lsmr, an un fliw ile sgl t q i a efec ive q 'ent miizi w er um a d i sx q s s c' q s ir lqvklfand; Ziwa yfn u rvr n vm a ti tia iuinf 'i that f her o e the surface ofjametallicbody compnising anyoneor more of these metals is removed in averyuni-form manner respectiveof the original surface contour ofthemetal; object beingdissolved "litre attack-is so uniform, for example-that sheets of zirconium 0. 04( thiclg canbe re duce d to-sheets.001"? to .jOQZfthickiDOOS" by-treat m ent in a substantially neutralsolution of ammonium lluorideffor a period of 30 minutes. Solution ofthe metal can be effectively carried out under widely differ- 2 qn itiqn9 ne vs s l e m e. a-s u qn of -ammonium fluoride havingga concentrationof 5 00 am Pe liter st ea tem ratu (25 i C-mn ma -1 othercase usinganammonium fluoride solution having a concentration of: 100 grams perliter at-a temperature of 9? a T P of the a m ni m uqrid d ufi a remains-fairly constant for a given concentration and m era u e and tt mp ra rs ,f i mo e e ature to around Q Q. be between about 6 to 7 pH, wherea?r, t m e -amiss and e e a a e a r approaching the boiling point of the:solution, will be slightly lower, -i.e.; about 5 to 6 due to theformation of a 'smalllamounti of animoniiim bifiuor-ide in the solu fromspenttelen'ientscalls-for the dikolving of='the "entire a fuelelernentassemldly" in solutions whieh arestrongly acid; aftfi ivhich the'vaiious element's are separated and purified'by complex "andlengthyFchmicar precduresi Such strongly acil solu e very difiieult to "toanothe'1-method,the entire tion. jItcan therefore be said that thepresent process is ma w th h qs b e e t q dz r Q er tqq vt t PH b twe n5 a id TQ I i t-J lyt higher, Regardless of the=. specific temperaturegang sq i wi it' he. de1- ql a ith metal removal talces"placer uniformlyancl the dissolution rate can :be predetermined with an accuracy 'in theneiag borhood of a few ten-thousandths of an inch. On the basis of suc hfindings, we have been able td remova zirconium alloy cl-adding 0.031"thick rwin clear fuel element without anyappreciable attackingof'tli'encased uraniumialloy' core materialoftliefeleinent by mersion ofthe'clad fuel'el'e'r'nen in a neutralsoliitionbf ammonium fluoride andre ova-armeue15ae1men (3) The alkali metals group, such as cesium.

from the ammonium fluoride solvent'solution after apre determined timebased upon the predictable rate of solution of the zirconium alloycladding under the tempera; ture and'concentration conditions of theammonium fluoride bath. Removal of the zirconium alloy or other corrosion-resistant metal cladding from the fuel element leaves the core ofthe element containing the nuclear fuel material in a 'substantia llyexposed condition suitable for further treatment for separation andrecovery of valuable constituents contained in the .core for furtheruse. 'Ihe dissolved zirconium contained in the ammonium fluoride 7solution also can be recovered by suitable'chemical proc essing aswillbe explained later. 7

Although the present process is described primarily as it is usually,and preferably, carried out with the use of substantially neutral orslightly acid solutions of 'am-, monium fluoride (NH F) because of thegreater ease of handling and containing such substantially neutral ormildly acidsolutions, ammonium bifluonide, NH' ,I-I=F ','of

high acidity, can similarly be used. Example VI herein is an example ofthe process as carried out utilizing an ammonium biliuOride solution asthe solvent.

We have further discovered that uranium and alloys of uranium andzirconium are soluble in substantially neutral solutions of ammoniumfluoride with both metals going into solution! As a; result, neutralsolutions of ammonium fluoride can therefore not onlyvbe usedeffectivelyfor the removal of the corrosion-resistant metal claddingsfror n'clad fuel elements but the same solutions can be'satisfactorilyused for the subsequent-processing of the fuel element core to recoverthe unused portion of nuclear fuel materiall contained in the core. iAfter the neutral "solution of ammonium fluoride has been used as asolvent medium for the disintegrationlor dissolution of thezirconium-uranium alloy, upon either c'oolingof' the fluoride solutionand/or the addition of ammonium fluoride to increase-the concentration,mixed crystals-of an ammonium fluozirconate, (NI-I 3ZI'F7, and uraniumfluoride are produced so that the zirconium and 7 tion and can then beseparated as explained herein. How

ever, when theuranium fluoride isdissolved in an ammonium fluoridesolution and the solution contains no zirconium the dissolved uraniumfluoride resists all eflorts to crystallize it out of solution. Thiseffect of zirconium uponthe behavior of the uranium fluoride is mostsurprising and we can offer no explanation for it. 1'

'When a fuel'element has served its useful life in a re actor itcontains, in addition to theoriginal nuclear fuel material,'bothifertile and fissionable,' and any alloying metal of the core; a'quantityofnewly formed nuclear fuel and' an appreciable amount ofradioactive fission products; Upon "aging-the used fuel element for aperiod of time-to'perniit radioactive elements with short halflife todecay, a process which is customary, the ,list of re-,

mainingjradioactive fission products, while still large,

canbe classified into groupsthat are similar in chemical behaviors.These are: 7

1) The rare earth group.

(:2) The alkaline earth group, principally strontium. i

(4) The inert gases such as krypton and xenon. (5) The halides such asiodine. v (6) The group including zirconium.

The fuel element core also contains, either as originally.

present or as produced during operations as a consequence of the fissionreaction, fissionable elements such as U235 and U 233and plutonium Pu 239 and'fertile I materialsfsuch as U. 2 38 or thorium.. ,When the core ofr a used or spent fuel element is dissolved or disintegrated in aneutral solutionof, ammonium fluoride, these radio- V active fissionproducts andlvarious fissionable materials form insoluble fluorides orfluoride complexes, which can thenbe. removed from the ammonium fluoridesolution by filtration, centrifuging or' by other suitable procedure.Iodineand the inert gases are. removed as gas ina suitable ventilationsy-stem;- The plutonium-which is present with-*the'radioactivefission'products'can be separated- 7 from the remaining fission productsby slurrying the prew :cipitate -wit-h' water and a mild oxidizer andoxalic/acid V, whichconvertstheplutoniumto asoluble oxalate whicheffective solvent means for the treatment and separation" of the varioususable constituentsof-a spent fuel element V flow-sheet the varioussteps'of, a process in accordance is then separated fromtheiothermaterials which remain insoluble. Ammonium fluoride in substantiallyneutral 9 solutionis therefore an eflective solventwhich. can be usednot only for the removal of the corrosion-resistant,

metal cladding of a clad-fuel elemenflbut it is also an coreroithedirect treatment of an unclad fuel element FIGURE '1 of the drawingdepicts in the-form of a with'the present invention for the recovery ofnuclear tion of ammonium fluoride solution is increased. The

fuel materials and'other'valuable constituents-from usedor spent fuelelements consisting of a body or -.corefofa uranium-zirconium alloywhich has been used without a cladding or hasrbeen encased in azirconium alloy or other corrosion resistant metallic' cladding. L

- FIGURE "2 is a cross-'sectionof a clad-nuclear fuel element having acentralportion' and two side rails, the core of the elementbeingdisposed in the central portion thereofii FIGURE 3" is asectionofthe same element after dissolution of the'Cladding; 1 The process oftreating a used or spent fuel element of Ithe'clad type in accordancewiththe procedure outlinedin FIGURE'l is as follows: Y

: After a suitable period 'of-aging to eliminate or'at least minimizethe content of radioactive fission products of short half-life in orderto reduce :as, much, as possible the hazards of handling anddifficulties of processing, the used fuelelem'entisimmersedin asubstantially neutral ammonium, fluoride solution and left in the solu-.

tion a sufiicient period of t ime jto removeisubstantially all thezirconium or zirconium.al1oy' cladding from the element,;therebyexposingnthe core ,Ofjh element for treatment.

The temperature and concentrationof the neutral ammonium fluoridesolution are not critical. al-

thoughithe rate of solution of the zirconium or zironium alloy claddingis dependent upon both. The temperature can rangefrorn room temperatureto in'the neighborhood'pofflthe,boilingpoint of the ammonium fluoridesolution and: the concentration can rangefrom 10% to over 50%. Therateof dissolution of Itheizirconium cladding increases.asthestem eratureand/or concentrarate of dissolution of: the zirconium or=zirconium1alloy in substantially .Aneutral ammonium fluoride solutions r nse itromagvery :low' rate of onlya few tenths of a mil-r per hour using ammoniumfluoride solutions of weak or lowcon centrationl atroom-temperature (250.); up a to adissolutionof welljover 1090 mils -;-per hour using;

ammoniunfflu ride solutions I of high concentration (over 40%) at anoptimum temperature at or nearrthe boiling temperature of the solution.When the cladding has been removed from the core of the fuel elementjitis removed for-processingzof thecore materials: ,"Afterthe ammoniumfluoride solution has been'iu' use forisome utime, and contains asubstantial amount of dissolved zirco nium, the zirconium can beremovedvfromathe solution by .either cooling; theisolution to. throw.down the Zcrystals crystals orconcentrated solutions to the usedammonium fluoride solution and cooling, or evaporating and cooling.

to. increase the ammonium fluoride concentration. The

ammonium fiuozirconate crystals can thenbe dissolved.

'Rturning'to the fuel element from which the zircoa niumcladding hasbeen stripped, the. declad fuel element is immersedjinasubstantiallyjneutral ammonium fluoride' so1ution wherein it isdisintegrated by' dissolution, resultifig in a solution containing th'edissolved uranium and wzir'conium constituents and 'an insoluble sludgeconsisting ,offthe' hot or radioactive fission products, in.- cludingthei'-rare earths, cesium, strontium: and barium, and also. plutonium.Anumb'er of the gaseous fission products ,such' as xenon,jkrypton,-iodine and the like pass ofiiiasgasesz The resultingsolution is filteredto remove the insolubl'es and-the. filtrate containing the .solubleuranium and zirconium fluorides or fluoride com plexes either cooledand/or additional ammonium fluoride'jadde'd' to the solution whereuponthe uranium and zirconiu'mzfluoridesi crystallize out of solution. Theinsolublefluoride's or fluoride complexes of 'the-h0t "or radioactivefissionproducts can be removed from the ammonium .fiuoride solution by 7continuous filtration.

Theexact nature of the zirconium and uranium compounds in solutionis notknown except that they are undoubtedly combined with'fluorine toform'complex ions; however, atcertain'ammonium fluoride, zirconium anduranium concentrations, (NH ZrF containing UF .XNH F.YH O. (where X +Yis equal to or greater than'O) crystallizedv from the solution 'as greencrystals. Since uranium "tetrafluoride is known to be green in colorwhereas all the "zirconium complexes "are colorless; the greerrcolor isattributed 'tothe-uranium.- These crystals are'separated from theammonium fiuoride-solu tion-by filtration: Upontreatment of theseparated crystals with distilled water, the zirconiumportion may becompletely 'dis'solvedleaving behind'deuse; crystalline uraniumtetrafluorideg- UF which is-insoluble. The separated ammonium'fluozirconateisolution is substantially free from uranium;

The a residual green crystals: of uranium 'tetraflu'oride, UF ,-.can:'beconverted 102 anoxidetby'any one of:rseveral-methods..w Forsexample,the: fluoridencan'bedissolved -.in:. nitric-acid :andra hydrousuranium-"oxide precipitated with} ammonia.- The-hydrous I oxide-canzthen be-ignited at 900 C. to-the uranium oxide, U o wvhich is :a-,black--powder. It .is considered thatthe separation and recovery ofuranium is fairly complete in that the resulting ,uranium; is ,.free,from; zirconium. and other metals; f

The precipitate obtained from the ammonium fluoride solution upondissolution of the fuel element core consists oftheinsolublefluorides"orfluoride complexes of plutonium, the rareearths, barium'and*strontiumyand the" complex fluorides of the alkalimetals;- presumed to be of the type =A MFg where- A is lithium; sodium,potassium, cesium, and rubidium and M is zirconium: The 'precipitateisslurried withfiwater and a mild oxidizer It is preferred The.zirconium hydrate is calcined.

added whereupon the plutonium is converted to the tetravalent state.Thez-addi'tion of soluble compoundcom taining theoxalate radical such asoxalic acid or amnio nium oxalate converts the plutoniumto a soIubleoxalate which is then separated in the motherliquor by filtration;

The plutonium because. of. its-value as. amauar'fuer material isrecovered by chemicalipi'oces'siug lin accord ancewithwell-knownprocedures; The remaining; ri' soluble radioactive sludgeisready forfsparaterecoverjyf or storage in underground tanks. I,

The following: examples are set forthin order mommy illustrate thespecifioways in which th'e'pfseiit process" can be carried out for thedecladdingof nuclear fuel el' ments and the recovery ='and1'separationof the valuable constituents of-the'core from the undesirableradioactivefission: products. v

Example I A section of a nuclear 'fuelelement such as that'sho'wirinFIGUR-E 2 wasused. The fuel element consisted" of a fuelplate =4 of-"auranium-zirconium alloy encased in' a= cladding 5 ofa zirconiumalloysuch as Zircaloy :2. The fuel element is also provided withsid=rails='6 "and73 The core of the-fuel elementis*0'.03-l""thi'c'k"-and the Zir: caloy 2 cladding is 0.030 thick. Theoverall thickness at the side rails of the fuelelemeufis 0.185.

A section o-f'a fuel plate of the abov'e de'scribed: type was "immersedinan ar'nmonium' fluoride solution .ofizap'i proximately 20% (200' gramsper liter) Tconcentration at l00-C., the solution =havinga pH -of '7.The Ziroaloy' cladding was diss'olved'from'all-the surfaces ata uniformrate of 1 mil per minute. A- coating ofm'ateriahinsoluble inthe-ammoniumfluoridebut completely soluble iii-dilute sulfuricacid-ammonium fluoride -solution"was formed: This coating did not appearto affect the rate of dissolution of the Zircaloy in theammon'iumfluoride solution. It appeared to be metallic and-is believed tobethe'tin portion of theZircaloy-nrateri al; it did not adheretightly to thespecimen and couldzbe-washed'oii After-the cladding was removed, thesection'of the fuel plate-had the appears ance shown in FIGURE 3 of'thedrawing The-fins 6a and. 7a constituting .the remnants of I thewsiderails -were readily severable from the remaining 'undissolved core-4;leaving the latter ready for further processing;

Example :11

Pieces of fuel element firee from Zircaloy 2 cladding were dissolved ina hot 20% (200 grarns'per liter) solu-: tion of=-ammonium fluoride at 7pH;- Upon coolinga green crystalline-material formed, and'was separated.The ammonium fluoride solution was made strongly alkaline with ammoniaand avoluminous precipitate resulted. Thisproved to be zirconium hydratecontaining an esti; mated 0.01% -or-less of uranium. Thisindicates thatthe uranium wasalmostj-completely contained. in the green crystals. r Jr The green crystals were dissolved in a minimum amount of distilledwater at C. and the solution cooled to 25 9 C. ,Uponfiltering the greencolor remained on the filter;- the solution was. water-white. Thefiltratecom ,tained only-zirconium, the green filter residue containedonly uranium asthe metal components.

We have noted that:

( 1)' These green uranium-bearing crystals a'reve'ry slightly soluble incoldwater," cold hydrofluoric acid solutions and 1 cold ammoniumfluoride solution'sx:

(2) They are easilyoxidized by nitiricacid-*andtyielda 7 yellowsolution;- r

(3) -Upon adding excessammonia to the-nitricacid solu= tioma canaryyellow 'uraniurmoxideiis precipitated;

( 4)" The =yellowoxide,-when separatedcby filtnation is'zireconiiim-fireew (5) Upon caloination at 900 'C.,' black U505, isproduced;

' Example' m A section of fuel plate of the type showninFIGURE 2 1 /2'long'and weighing44.l096 was immersed in a (150:grams per liter)substantially neutral solutionof ammonium fluoride at 103 C;; after100'minutes in the solution, 16.5752 grams of metal remained. The

rate ofsolution was 30 mils'in one hundred 'minutes or' l8 milsper hour.58'mils were removed in the center section 01129 mils per side, and 62from the side rails or 31 per side. i The dissolution of metal wasextremely uniform over the entire surface; the treated specimenconsisting of the core of nuclear fuel material com-.

' pletely free from the Zircaloy cladding with the side rails attachedis shown in FIGURE 3 ofthe drawing. r I

Example IV v A segment of fuel plate similar to that used in Example IIIand weighing 38.0683 grams was immersed in a substantially neutralsolution of ammoniumfluoride of .(200 grams per liter) concentration forone hour at the boiling point (about, 105 C.). The resulting finned butdecladded plate weighed 9.69 grams, showing a removal of 31 mils fromall surfaces.- The surface area tofjthe Example VI A'Segment of fuelplate similar to that used in Example V and weighing 44.5431 grams wasimmersed in axneatr boiling solution of ammonium bifluoride; Thetemperature of the solution was maintained at 180 C. a After two minutesin this solution, the thickness of the specimen was reduced from 0091"to 0.027", corresponding to a loss of approximatelylS mils per minute oneach surface.

The weight of the specimen after treatment was 14.4147

grams. This fast etch wasextremely uniform in that the,

thickness of the etched plate varied less than 1 mil.

While we have particularly described the invention as it has beenapplied to the treatment of fuel elementsembodying a zirconium orzirconium alloy cladding, the invention is similarly applicable to theprocessing of nuclear fuel elements of the non-clad solid type. It isalso applicable to fuelelements embodying plutonium as the nuclear fuelmaterial. It is also obvious that the process is'equally' effectivewith-all shapes and sizes of fuel elemerits, and not limited to anyspecific form such as the plate form shown in FIGURES 2 and 3 of thedrawing. Having described the invention in detail it is desired toclaim: p a

1. In a process for recovering the coreof a clad nuclear fuel element ofthe solid type by the removal of the cladding therefrom, wherein thenuclear fuel element is of the type having ametalli'c core ofnuclearfuel mate rial consisting of a thermal neutron fissionablematerial that is selected from the group consisting of the thermalneutron fi'ssionable uranium isotopes, plutonium, "and mixtures thereof,and a metallic material selected fromjthe group consisting of zirconiumand alloys consisting preponderantly of zirconium, and disposed aboutthe'core, a cladding of corrosion-resistant zirconiumrbased" metalpreponderantly of zirconium, the steps comprising immersing the cladelementin a substantially neutral'soluelement in the ammonium fluoridesolution, and then removing the core from the solution and therebyrecovering the core free from the cladding. I

2. Aprocess according to claim 1 in which the c ding is zirconium. a

' integrating said element therein by dissolutiontof the'solu -10%im50'% .7 a t a 5.- A processaccording'toclaim 1' in whichthe' ammoni umfluoride solution is maintained at a temperature be .,3'-fA processaccordingijto claim '1 in which thecla'd ding is" a-- zir c0niumalloy-l-preponderantly' of "zirconium; A'process according to claim 1 inwhich the concentration oflthe ammonium fluoride solution is fromi ttween '25 C and the boilingij'p'oint of the solution. 7

6, In a process for the recoverypf the valuable components of the coreof a nuclearfuel element of the solid type having a metallic corejof'nuclear.fueljmaterial consisting of athermalneutron fissionablematerial. selected 7 from the group 'co'nsist'in'g'of thei'thermalneutron fission able uranium isotopes, plutonium, andjmixtures thereof,andametallic material selected from the group consisting of zirconiumand alloys consisting}preponderantly ofi zirconium, and encasingsaid'core, a cladding of cor-"f rosionfresistant zirconium-based metalpreponderantly' of zircon um, the steps comprising stripping thecladding from said element 'to'expose the core, immersing the exposedcore in a substantially neutral solution'of ammoni-. V um fluor1de, 'and disintegratingthe core? by; dissolution thereinf f 7. A processf forthe recovery of the 'valuable compcfi nents of a nuclear fuel elementofthe solid type, having a metallic core' oft nuclearifuel' imaterialconsisting of a V a thermal neut'ron fis'sionable materialselectedffrom' the; 7

group consistingfof the thermal neutron fissionable ura'ni-j 1 mnisotopes, plutonium, and: mixturesthereofgfand a inc-f tallrc --materialselected from the group consisting offzirt comum andalloysconsisting'preponderantly of zirconi um, and, encasing saidcore, acladding of corrosion-resistant zirconium-based metal preponderantly ofzirconi- 1 1.111, the steps comprising immersing said element in, asubstantially neutral solution of ammonium'fl'uoride, dis-j ble metallicconstituents thereofin the solution, and then separatmg fr'om the,remaining constituents of the Solutlon thetther'mal neutron'fissionablematerial values.

8. A process according to, claim 7 in which the concentration .of theammonium fluoride solution is from 10%.t'o'50 duringsaid'disintegratingstep. t V

. 9. Aproce'ss' accordinglto'claim 7 in which the ammonium-fluoridesolution is maintained between 25 C and the boiling point of saidsolution'during said disintegratingstep. g V p a j 10. A processfor therecovery of theyaluable components of a nuclear fuel element-of thesolid type having a metallic-core of nuclear fuel material consisting ofa thermal neutron fissionablematerialselected from thegroup consistingof :the thermal'neutron fissionable urani- V um isotopes, plutonium, andmixtures thereof, a A

metallic material selectedfrom the'group consisting of zirconiumand'alloys consistingjpreponderantly of zirconium, and, encasingsaid'core,'a cladding of corrosionresis'tant 1 zirconium-based metal Qpreponderantly 10f zirconium, the steps comprising immersing the cladelement in 'asubstantiallyneutral'solution of ammonium fluoride,dissolving said 'cladding'from the 'element'insaid ammo nium fluoridesolutionfo expose the core,1 removingthe exposed core undissolved' fromthe ammonium fluoride solutionicontaining the dissolved cladding,immersing said core in another substantiallygneutral solution'of niumfluoride and disintegrating said core therei'n by dis solution. i I

' 11. A process'accordinglto claim 10 in'which thecladding metal-is azirconium, alloy preponderantly of zir-.-

co'niumQ 12. A process according to claim l0 in" which the claddingmetalis zirconium; 7 t 1 3 A process according to claim 10in which theconcentration of the' ammonium; fluoride solution is from 14. A processaccordi m claim .10 in which the ammonium fluoride solution ismaintained between 25 C- and the boiling point of the solution.

15. In a process for recovering the valuable components of a usednuclear fuel element of the solid type having a metallic core of nuclearfuel material consisting of a thermal neutron fissionable materialselected from the group consisting of the thermal neutron fissionableuranium isotopes, plutonium, and mixtures thereof, radioactive fissionproducts, and a metallic material se lected from the group consisting ofzirconium and alloys consisting preponderantly of zirconium, and,encasing said core, a cladding of corrosion-resistant zirconiumbasedmetal preponderantly of zirconium, in which process the core of theelement is disintegrated by solvent action in a substantially neutralsolution of ammonium fluoride to obtain insolubles including theplutonium values and a solution including fluorides of zirconium anduranium, the method for separating the uranium and plutonium values fromthe said insolubles and the resulting fluoride solution by stepscomprising: separating said insolubles from the fluoride solution, thenadding ammonium fluoride to the solution and cooling the solution toprecipitate contained fluorides of zirconium and uranium, separating theprecipitated fluorides of zirconium and uranium from the solution,adding Water to the separated mixture of zirconium and uranium fluoridesto dissolve the zirconium fluoride, separating the undissolved uraniumfluoride from the resulting solution, slurrying the aforesaid insolublesfrom the initial solution separation with Water in the presence of anoxidizing agent to oxidize the plutonium constituent thereof, thenadding thereto an oxalate compound to form a soluble plutonium oxalate,and separating the remaining insolubles therefrom to recover theplutonium.

16. In a process for recovering the valuable components of a usednuclear fuel element of the solid type having a metallic core of nuclearfuel material consisting of a thermal neutron fissionable materialselected from the group consisting of the thermal neutron fissionableuranium isotopes, plutonium, and mixtures thereof, radioactive fissionproducts, and a metallic material selected from the group consisting ofzirconium and alloys consisting preponderantly of zirconium and,encasing said core, a cladding of corrosion-resistant zirconium-basedmetal preponderantly of zirconium, in which process the metallic core ofthe element is disintegrated by solvent action in a substantiallyneutral solution of ammonium fluoride to provide a resulting solution ofsoluble fluorides including zirconium fluoride and uranium fluoride andto cause the precipitation of insolubles including fluorides andfluoride complexes of radioactive fission products and plutonium, thesteps comprising treating the insoluble fluoride mixture in an aqueousslurry with an oxidizing agent to oxidize the plutonium constituent,adding an oxalate compound to the oxidized solution to convert theplutonium constituent to a soluble plutonium oxalate, and separating thesolution from the insoluble radioactive residue.

17. In the process of recovering the valuable components of the metalliccore of a nuclear fuel element of the solid type in which said coreconsists essentially of a thermal neutron fissionable material selectedfrom the group consisting of the thermal neutron fissionable uraniumisotopes, plutonium, and mixtures thereof, and a metallic materialselected from the group consisting of zirconium and alloys consistingpreponderantly of zirconium, and in which the metallic core of theelement is disintegrated by solvent action in a substantially neutralsolution of ammonium fluoride to obtain an insoluble precipitate and asolution including the fluorides of zirconium and uranium, the stepscomprising recovering mixed crystals including zirconium and uraniumfluorides from said last-named solution, slurrying said mixed crystalsin water to dissolve the zirconium-containing portion thereof, andseparating the insoluble uranium-containing portion thereof.

18. In the process of recovering zirconium from the cladding of anuclear fuel element of the solid type hav ing a metallic core ofnuclear fuel material consisting of a thermal neutron fissionablematerial selected from the group consisting of the thermal neutronfissionable uranium isotopes, plutonium, and mixtures thereof, and ametallic material selected from the group consisting of zirconium andalloys consisting preponderantly of zirconium, and, encasing said core,a cladding of corrosionresistant zirconium-based metal preponderantly ofzirconium, and in which process the cladding is dissolved from theelement in a substantially neutral solution of ammonium fluoride, themethod of recovering the zirconium values from the resulting solutionwhich comprises adding suflicient ammonia to the solution to raise thepH of the solution to 8 to 9, thereby forming insoluble zirconiumhydrate, and separating the insoluble zirconium hydrate from thesolution.

19. In the process of recovering zirconium from the cladding of anuclear fuel element of the solid type having a metallic core of nuclearfuel material consisting of a thermal neutron fissionable materialselected from the group consisting of the thermal neutron fissionableuranium isotopes, plutonium, and mixtures thereof, together with ametallic material selected from the group consisting of zirconium andalloys consisting preponderantly of zirconium, said core being encasedin a cladding of corrosion-resistant zirconium-based metalpreponderantly of zirconium, and in which process the cladding isdissolved from the element in a substantially neutral solution ofammonium fluoride, the method of recovering the zirconium values fromthe resulting solution and of regenerating the solution for further use,comprising adding sufficient ammonia to said resulting solution to raisethe pH of the solution to 8 to 9, thereby forming insoluble zirconiumhydrate, separating the insoluble zirconium hydrate from the solution,stripping the ammonia from the solution, and then concentrating thestripped solution for reuse in the process.

References Cited in the file of this patent UNITED STATES PATENTS McCordet a1. Jan. 19, 1960 OTHER REFERENCES UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,007,769 November 7 1961 Andrew T.McCord et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

I 7 Column 7, line 7O, after "solu" insert tion of 1 ammonium fluoride,dissolving the cladding of the Signed and sealed this- 24th day of April1962.

(SEAL) Attest:

ESTON G. 'JOHNSON DAVID L. LADD Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,007, 769 November 7 1961 Andrew T. McCord et al.,

It is hereby certified that error appears in the above numbered patentrequiring correction and that th e said Letters Patent should read ascorrected below.

Column 7, line 70, after "solu" insert tion of ammonium fluoridedissolving the cladding of the Signed and sealed this 24th day of April1962.

(SEAL) Attest:

ESTON Go JOHNSON Commissioner of Patents

1. IN A PROCESS FOR RECOVERING THE CORE OF A CLAD NUCLEAR FUEL ELEMENTOF THE SOLID TYPE BY THE REMOVAL OF THE CLADDING THERERROM, WHEREIN THENUCLEAR FUEL ELEMENT IS OF THE TYPE HAVING A METALLIC CORE OF NUCLEARFUEL MATERIAL CONSISTING OF A THERMAL NEUTRON FISSIONABLE MATERIAL THATIS SELECTED FROM THE GROUP CONSISTING OF THE THERMAL NEUTRON FISSIONABLEURANIUM ISOTOPES, PLUTONIUM, AND MIXTURES THEREOF, AND A METALLICMATEIAL SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM AND ALLOYSCONSISTING PREPONDERANTLY OF ZIRCONIUM, AND DISPOSED ABOUT THE CORE, ACLADDING OF CORROSION-RESISTANT ZIRCONIUM-BASED METAL PREPONDERANTLY OFZIRCONIUM, THE STEPS COMPRISING IMMERSING THE CLAD ELEMENT IN ASUBSTANTIALLY NEUTRAL SOLUELEMENT IN THE AMMONIUM FLUORIDE SOLUTION, ANDTHEN REMOVING THE CORE FROM THE SOLUTION AND THEREBY RECOVERING THE COREFREE FROM THE CLADDING.